The present invention generally relates to refrigeration equipment and, more particularly, is concerned with a heat transfer core for an air cooling apparatus comprising an annular stack of spaced-apart finless, hollow coils of flattened oval shape in cross-section for improved sanitation and air flow efficiency.
In meat and other food processing installations, it is necessary to maintain the temperature of the processing room at a relatively low level to prevent the growth of bacteria. In order to cool food processing facilities of this type, large evaporator coils are typically mounted near the ceiling and air is circulated through them to maintain the temperature of the facility at an acceptably low level. One type of prior art evaporator comprises a plurality of finned tubes in a rectangular configuration wherein the tubes are positioned in staggered relationship to the flow of air. The reasoning was that the staggered arrangement would produce better contact between the flowing recirculating air and the heat exchanger tubes.
A further type of prior art heat exchange coil is shown in U.S. Pat. No. 4,615,176, in the name of the inventor herein. This heat exchange coil unit comprises a plurality of finned stainless steel coils arranged in an annular fashion with rows of individual coils in radial alignment and the coils being stacked in vertical, axial alignment. In this heat exchanger unit, the tubing of the coils is circular in transverse cross-section.
A problem with both the rectangular and annular prior art evaporators is that the static and velocity pressures, which are a measure of the resistance to air flow through the heat exchanger, are relatively high thereby requiring the use of larger motors to move a given volume of air through the coil stack. In the case of the rectangular heat exchanger, the staggered arrangement of the individual coils or tubing causes the air to flow in a tortuous path through the unit. In one prior art rectangular condenser, the tubes are flattened to an oval shape, but the tubing is arranged in a staggered pattern, thereby providing the high static and velocity pressures referred to above. In the case of round cross-section tubing, even if it is arranged in straight rows and columns, the flow of air across it will be quite turbulent as air streams encounter the arcuate surfaces and thus change direction several times to flow past and around any given tube. This results in a speeding up and slowing down of the air flow around the tube, which greatly increases static pressure due to the resulting turbulence.
Refrigeration equipment is typically employed for cooling meat and food products to retard bacterial growth thereon. Facilities used for meat and food product processing must adhere to strict sanitation requirements. Heretofore, the refrigeration equipment was not likely to be considered when steps were taken to improve sanitation conditions. One reason for this oversight was because the selection between different refrigeration equipment was limited in view that most incorporated a stack of galvanized coils with closely spaced fins on their exterior. The finned galvanized coils have many cracks and crevices for bacteria to grow in and there are areas difficult to clean.
To prevent outbreaks of contamination, the food industry has been looking for innovative ways to combat bacteria growth. Part of the invention herein is the recognition by applicant that coil stack design for refrigeration equipment should be considered together with other measures to improve sanitation at meat and food processing facilities. Along with energy and cooling efficiency, the capability of cleaning the coil bundle and of it remaining clean for an extended period of use, without adversel affecting operating efficiency, should be an important performance objective. Consequently, a need exists for an alternative coil bundle or stack construction which will improve sanitation conditions while, at a minimum, maintaining present energy and cooling efficiencies.